| Message ID | 1458545443-3302-1-git-send-email-daniel.vetter@ffwll.ch (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 21 March 2016 at 13:00, Daniel Vetter <daniel.vetter@ffwll.ch> wrote: > Just a bit of wording polish plus mentioning that it can fail and must > be restarted. > > Requested by Sumit. > > Cc: Chris Wilson <chris@chris-wilson.co.uk> > Cc: Tiago Vignatti <tiago.vignatti@intel.com> > Cc: Stéphane Marchesin <marcheu@chromium.org> > Cc: David Herrmann <dh.herrmann@gmail.com> > Cc: Sumit Semwal <sumit.semwal@linaro.org> > Cc: Daniel Vetter <daniel.vetter@intel.com> > CC: linux-media@vger.kernel.org > Cc: dri-devel@lists.freedesktop.org > Cc: linaro-mm-sig@lists.linaro.org > Cc: intel-gfx@lists.freedesktop.org > Cc: devel@driverdev.osuosl.org > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com> Acked-by: Sumit Semwal <sumit.semwal@linaro.org> > --- > Documentation/dma-buf-sharing.txt | 11 ++++++----- > drivers/dma-buf/dma-buf.c | 2 +- > 2 files changed, 7 insertions(+), 6 deletions(-) > > diff --git a/Documentation/dma-buf-sharing.txt b/Documentation/dma-buf-sharing.txt > index 32ac32e773e1..5c4e3e586ec8 100644 > --- a/Documentation/dma-buf-sharing.txt > +++ b/Documentation/dma-buf-sharing.txt > @@ -352,7 +352,8 @@ Being able to mmap an export dma-buf buffer object has 2 main use-cases: > > No special interfaces, userspace simply calls mmap on the dma-buf fd, making > sure that the cache synchronization ioctl (DMA_BUF_IOCTL_SYNC) is *always* > - used when the access happens. This is discussed next paragraphs. > + used when the access happens. Note that DMA_BUF_IOCTL_SYNC can fail with > + -EGAIN or -EINTR, in which case it must be restarted. > > Some systems might need some sort of cache coherency management e.g. when > CPU and GPU domains are being accessed through dma-buf at the same time. To > @@ -366,10 +367,10 @@ Being able to mmap an export dma-buf buffer object has 2 main use-cases: > want (with the new data being consumed by the GPU or say scanout device) > - munmap once you don't need the buffer any more > > - Therefore, for correctness and optimal performance, systems with the memory > - cache shared by the GPU and CPU i.e. the "coherent" and also the > - "incoherent" are always required to use SYNC_START and SYNC_END before and > - after, respectively, when accessing the mapped address. > + For correctness and optimal performance, it is always required to use > + SYNC_START and SYNC_END before and after, respectively, when accessing the > + mapped address. Userspace cannot on coherent access, even when there are > + systems where it just works without calling these ioctls. > > 2. Supporting existing mmap interfaces in importers > > diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c > index 774a60f4309a..4a2c07ee6677 100644 > --- a/drivers/dma-buf/dma-buf.c > +++ b/drivers/dma-buf/dma-buf.c > @@ -612,7 +612,7 @@ EXPORT_SYMBOL_GPL(dma_buf_begin_cpu_access); > * @dmabuf: [in] buffer to complete cpu access for. > * @direction: [in] length of range for cpu access. > * > - * This call must always succeed. > + * Can return negative error values, returns 0 on success. > */ > int dma_buf_end_cpu_access(struct dma_buf *dmabuf, > enum dma_data_direction direction) > -- > 2.8.0.rc3 > Best regards, Sumit.
On Mon, Mar 21, 2016 at 8:40 AM, Hans Verkuil <hverkuil@xs4all.nl> wrote: >> + For correctness and optimal performance, it is always required to use >> + SYNC_START and SYNC_END before and after, respectively, when accessing the >> + mapped address. Userspace cannot on coherent access, even when there are > > "Userspace cannot on coherent access"? Do you mean "cannot do"? Sorry, the > meaning isn't clear to me. "cannot rely on". I'll send out v2 asap (and let's hope the coffee works this time around). -Daniel
diff --git a/Documentation/dma-buf-sharing.txt b/Documentation/dma-buf-sharing.txt index 32ac32e773e1..5c4e3e586ec8 100644 --- a/Documentation/dma-buf-sharing.txt +++ b/Documentation/dma-buf-sharing.txt @@ -352,7 +352,8 @@ Being able to mmap an export dma-buf buffer object has 2 main use-cases: No special interfaces, userspace simply calls mmap on the dma-buf fd, making sure that the cache synchronization ioctl (DMA_BUF_IOCTL_SYNC) is *always* - used when the access happens. This is discussed next paragraphs. + used when the access happens. Note that DMA_BUF_IOCTL_SYNC can fail with + -EGAIN or -EINTR, in which case it must be restarted. Some systems might need some sort of cache coherency management e.g. when CPU and GPU domains are being accessed through dma-buf at the same time. To @@ -366,10 +367,10 @@ Being able to mmap an export dma-buf buffer object has 2 main use-cases: want (with the new data being consumed by the GPU or say scanout device) - munmap once you don't need the buffer any more - Therefore, for correctness and optimal performance, systems with the memory - cache shared by the GPU and CPU i.e. the "coherent" and also the - "incoherent" are always required to use SYNC_START and SYNC_END before and - after, respectively, when accessing the mapped address. + For correctness and optimal performance, it is always required to use + SYNC_START and SYNC_END before and after, respectively, when accessing the + mapped address. Userspace cannot on coherent access, even when there are + systems where it just works without calling these ioctls. 2. Supporting existing mmap interfaces in importers diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index 774a60f4309a..4a2c07ee6677 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -612,7 +612,7 @@ EXPORT_SYMBOL_GPL(dma_buf_begin_cpu_access); * @dmabuf: [in] buffer to complete cpu access for. * @direction: [in] length of range for cpu access. * - * This call must always succeed. + * Can return negative error values, returns 0 on success. */ int dma_buf_end_cpu_access(struct dma_buf *dmabuf, enum dma_data_direction direction)
Just a bit of wording polish plus mentioning that it can fail and must be restarted. Requested by Sumit. Cc: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tiago Vignatti <tiago.vignatti@intel.com> Cc: Stéphane Marchesin <marcheu@chromium.org> Cc: David Herrmann <dh.herrmann@gmail.com> Cc: Sumit Semwal <sumit.semwal@linaro.org> Cc: Daniel Vetter <daniel.vetter@intel.com> CC: linux-media@vger.kernel.org Cc: dri-devel@lists.freedesktop.org Cc: linaro-mm-sig@lists.linaro.org Cc: intel-gfx@lists.freedesktop.org Cc: devel@driverdev.osuosl.org Signed-off-by: Daniel Vetter <daniel.vetter@intel.com> --- Documentation/dma-buf-sharing.txt | 11 ++++++----- drivers/dma-buf/dma-buf.c | 2 +- 2 files changed, 7 insertions(+), 6 deletions(-)